Accounting for Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	$ 115,951	$ (44,872)	$ (24,853)	$ (2,097)
Included in earnings	180,533	(15,839)	(23,559)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Regulatory Assets (Liabilities)	301	(1,749)	(1,049)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	(20,603)	(2,431)	1,852
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers into Level 3	0	0	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3	$ 592	0	0
Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Unrealized (gain) loss on derivative instruments, net
Subsidiaries [Member]
Derivative [Line Items]
Hedging strategy number of years extended	3 years
Natural Gas Portfolio
Derivative [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	$ (127)	(2,120)	(1,135)	1,282
Included in earnings	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Regulatory Assets (Liabilities)	301	(1,749)	(1,049)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	1,369	764	(1,368)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers into Level 3	0	0	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3	323	0	0
Electric Portfolio
Derivative [Line Items]
Posted Collateral	56,200	12,782
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	116,078	(42,752)	(23,718)	$ (3,379)
Included in earnings	180,533	(15,839)	(23,559)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Regulatory Assets (Liabilities)	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	(21,972)	(3,195)	3,220
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers into Level 3	0	0	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3	269	0	$ 0
Electricity, US Regulated [Member]
Derivative [Line Items]
Posted Collateral	23,200
Natural Gas, US Regulated [Member]
Derivative [Line Items]
Posted Collateral	$ 33,000
External Credit Rating, Investment Grade [Member]
Derivative [Line Items]
Percentage of derivatives with credit risk exposure	99.40%
External Credit Rating, Non Investment Grade [Member]
Derivative [Line Items]
Percentage of derivatives with credit risk exposure	0.60%
Credit Rating \| Natural Gas Portfolio \| Standby Letters of Credit
Derivative [Line Items]
Posted Collateral	$ 28,000
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases	50,000
Credit Rating \| Electric Portfolio
Derivative [Line Items]
Posted Collateral	$ 0	$ 0

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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Regulatory Assets (Liabilities)

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Amount of gain (loss) recognized in income from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value on recurring basis using unobservable input (level 3).

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Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into level 3 of the fair value hierarchy.

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Indicates line item in statement in which net income is reported that includes gain (loss) from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value using unobservable input (level 3).

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